Nutritional Aspects of Malabsorption: Short Gut Adaptation

Changes of Drug Pharmacokinetics in Patients with Short Bowel Syndrome: A Systematic Review

BACKGROUND AND OBJECTIVES

Short bowel syndrome is a clinical condition defined by malabsorption of nutrients and micronutrients, most commonly following extensive intestinal resection. Due to a loss of absorptive surfaces, the absorption of orally administered drugs is also often affected. The purpose of this study was to systematically review the published literature and examine the effects of short bowel syndrome on drug pharmacokinetics and clinical outcomes.

METHODS

Studies were identified through searches of databases MEDLINE, EMBASE, Web of Science, and SCOPUS, in addition to hand searches of studies' reference lists. Two reviewers independently assessed studies for inclusion, yielding 50 studies involving 37 different drugs in patients with short bowel syndrome.

RESULTS

Evidence of decreased drug absorption was observed in 29 out of 37 drugs, 6 of which lost therapeutic effect, and 14 of which continued to demonstrate clinical benefit through drug monitoring.

CONCLUSIONS

The influence of short bowel syndrome on drug absorption appears to be drug-specific and dependent on the location and extent of resection. The presence of a colon in continuity may also influence drug bioavailability as it can contribute significantly to the absorption of drugs (e.g., metoprolol); likewise, drugs that have a wide absorption window or are known to be absorbed in the colon are least likely to be malabsorbed. Individualized dosing may be necessary to achieve therapeutic efficacy, and therapeutic drug monitoring, where available, should be considered in short bowel syndrome patients, especially for drugs with narrow therapeutic indices.

Short Bowel Syndrome: Clinical Guidelines for Nutrition Management

Intestinal failure is a condition in which inadequate digestion or absorption of fluid, electrolytes, and nutrients leads to dehydration or malnutrition. The most common cause of intestinal failure is short bowel syndrome (SBS) defined as <200 cm of functional small intestine. SBS may result from congenital abnormalities or from surgical resection. For the past 3 decades, patients with severe SBS were managed with home parenteral nutrition (HPN). With the emergence of new therapies, the clinician now has multiple options to treat these patients. These include intestinal rehabilitation regimens whereby patients are treated with specialized oral diets, soluble fiber, oral rehydration solutions (ORS), and trophic factors to enhance absorption. There are also a variety of surgical techniques available to preserve intestinal length. Small bowel and multivisceral transplantation has evolved during the last decade to be a valid therapeutic option for those patients who cannot be rehabilitated or who fail HPN. These are interrelated services designed to offer the patient the best therapeutic options to meet their individual needs. This article reviews the principles associated with the nutrition management of this very complex and diverse group of patients.

Prevalence of non-alcoholic fatty liver disease in four different weight related patient groups: association with small bowel length and risk factors

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is an obesity associated common cause of liver inflammation and there are concerns that it may turn out to be the most common cause of liver failure as prevalence of obesity increases. We determined the prevalence of NASH in relation to gender and body mass index (BMI). Furthermore, we assessed the association of NASH with the length of the small bowel.

METHODS

124 liver samples obtained during routine operations were examined looking for NAFLD Activity Score (nonalcoholic fatty liver disease). The length of small bowel was measured intraoperatively. For evaluation, patients were divided into four groups according to their BMI (group 1: normal weight, group 2: overweight, group 3: grade I/II morbidly obese, and group 4 grade III morbidly obese patients).

RESULTS

BMI showed a strong positive correlation with risk of NASH and a weak positive correlation with small bowel length. No normal weight patient was at risk of NASH, whereas in group 2 14% had uncertain and 32% definite NASH. In group 3 11% had uncertain and 27% definite NASH. In group 4 nearly two-thirds were classified as uncertain or definite NASH. Median length of small bowel in all patients was 450 cm (range 226-860 cm). Within group 4, patients with definite/uncertain NASH had a longer small bowel than patients without NASH.

CONCLUSIONS

Prevalence of NASH is high in morbidly obese. Small bowel length could influence the complex etiology of the disease.

Efficacy of the glucagon-like peptide-1 agonist exenatide in the treatment of short bowel syndrome

BACKGROUND

Short bowel syndrome (SBS) is a serious clinical disorder characterized by diarrhea and nutritional deprivation. Glucagon-like peptide-1 (GLP-1) is a key hormone, produced by L-cells in the ileum, that regulates proximal gut transit. When extensive ileal resection occurs, as in SBS, GLP-1 levels may be deficient. In this study, we test whether the use of GLP-1 agonist exenatide can improve the nutritional state and intestinal symptoms of patients with SBS.

METHODS

Five consecutive patients with SBS based on ≤90 cm of small bowel and clinical evidence of nutritional deprivation were selected. Baseline SBS symptoms, demographic and laboratory data were obtained. Antroduodenal manometry was performed on each subject. Each patient was then started on exenatide and over the following month, the baseline parameters were repeated.

KEY RESULTS

The subjects consisted of four males and one female, aged 46-69 years. At baseline, all had severe diarrhea that ranged from 6 to 15 bowel movements per day, often occurring within minutes of eating. After exenatide, all five patients had immediate improvement in bowel frequency and form; bowel movements were no longer meal-related. Total parenteral nutrition was stopped successfully in three patients. Antroduodenal manometry revealed continuous low amplitude gastric contractions during fasting which completely normalized with exenatide.

CONCLUSIONS & INFERENCES

Exenatide is a novel and safe treatment option for SBS. It produced substantial improvement in the bowel habits, nutritional status and quality of life of SBS patients. Successful treatment with exenatide may significantly reduce the need for parenteral nutrition and small bowel transplant.

Pediatric intestinal and multivisceral transplantation: a new challenge for the pediatric intensivist

INTRODUCTION

With increasing survival rates, intestinal transplantation (ITx) and multivisceral transplantation have reached the mainstream of medical care. Pediatric candidates for ITx often suffer from severe multisystem impairments that pose challenges to the medical team. These patients frequently require intensive care preoperatively and have unique intensive care needs postoperatively.

METHODS

We reviewed the literature on intensive care of pediatric intestinal transplantation as well as our own experience. This review is not aimed only at pediatric intensivists from ITx centers; these patients frequently require ICU care at other institutions.

RESULTS

Preoperative management focuses on optimization of organ function, minimizing ventilator-induced lung injury, preventing excessive edema yet maintaining adequate organ perfusion, preventing and controlling sepsis and bleeding from varices at enterocutaneous interfaces, and optimizing nutritional support. The goal is to extend life in stable condition to the point of transplantation. Postoperative care focuses on optimizing perfusion of the mesenteric circulation by maintaining intravascular volume, minimizing hypercoagulability, and providing adequate oxygen delivery. Careful monitoring of the stoma and its output and correction of electrolyte imbalances that may require renal replacement therapy is critical, as are monitoring for and aggressively treating infections, which often present with only subtle clinical clues. Signs of intestinal rejection may be non-specific, and early differentiation from other causes of intestinal dysfunction is important. Understanding of the expanding armamentarium of immunosuppressive agents and their side-effects is required.

CONCLUSIONS

As outcomes of ITx improve, transplant teams accept patients with higher pre-operative morbidity and at higher risk for complications. Many ITx patients would benefit from earlier referral for transplant evaluation before severe liver disease, recurrent central venous catheter-related sepsis and venous thromboses develop.

Short bowel syndrome: parenteral nutrition versus intestinal transplantation. Where are we today?

Current management of short bowel syndrome (SBS) revolves around the use of home TPN (HPN). Complications include liver disease, catheter-related infections or occlusions, venous thrombosis, and bone disease. Patient survival with SBS on TPN is 86% and 75% at 2 and 5 years, respectively. Surgical management of SBS includes nontransplant surgeries such as serial transverse enteroplasty and reanastomosis. Small bowel transplant has become increasingly popular for management of SBS and is usually indicated when TPN cannot be continued. Posttransplant complications include graft-versus-host reaction, infections in an immunocompromised patient, vascular and biliary diseases, and recurrence of the original disease. Following intestinal-only transplants, patient and graft survival rate is 77% and 66% after 1 year. After 5 years the survival figures are 49% and 34%, respectively. Future improvements in survival and quality of life will enhance small bowel transplant as a viable treatment option for patients with SBS.

Dietary and medical management of short bowel syndrome in adult patients

Resection of the small bowel can lead to malabsorption of fluid, electrolytes, minerals, and other essential nutrients, resulting in malnutrition and dehydration. Individualized and tailored nutritional management for patients with short bowel syndrome (SBS) helps to optimize intestinal absorption, leading to nutritional independence such that a patient can resume as normal a lifestyle as possible. Parenteral nutrition (PN), used to supply the required nutrients following resection, is associated with a number of complications affecting patient morbidity and mortality. Attempts should be made to wean patients from PN to an oral diet as soon as possible. Dietary management is complex and needs to be individualized for each patient on the basis of his or her specific gastrointestinal anatomy, underlying disease, and lifestyle. In addition to nutrient intake, management of SBS also requires appropriate oral rehydration, vitamin and mineral supplementation, and pharmacotherapy. Several medications provide a useful adjunctive function to dietary intervention, including antidiarrheal agents, H2 antagonists and proton pump inhibitors, pancreatic enzymes, somatostatin analogs, antimicrobials, and trophic factors.

Strategies for parenteral nutrition weaning in adult patients with short bowel syndrome

The development of parenteral nutrition (PN) was an important, life-saving advance in the care of patients with short bowel syndrome (SBS). Nevertheless, its long-term use is often associated with complications. Therefore, it is desirable, when possible, to wean SBS patients to an oral diet. Given the complexity of PN weaning and the lack of published guidelines, the purpose of this article is to describe strategies of PN weaning and illustrate important clinical considerations during the weaning process. Patient education and motivation are key factors in successful PN weaning. The patient should have clearly defined care protocols and understand the importance of each aspect of the weaning program. Other factors likely to influence weaning success include the length and health of the remnant bowel, the presence of a colon, and the degree to which bowel adaptation has occurred. It is imperative that daily oral fluid and caloric intake goals are met prior to initiating PN weaning and that the patient receives an optimized dietary and medication plan. During weaning, the most practical measures for assessing adequate hydration and nutritional status are oral intake, stool and urine output, serum electrolytes and visceral proteins, and body weight. PN reductions can be made by either decreasing the days of PN infusion per week or decreasing the PN infusion volume equally across all days of the week. Use of recombinant human growth hormone, with or without glutamine, may play a role in facilitating the PN weaning process.

Short bowel syndrome

Short bowel syndrome has significant morbidity and is potentially lethal especially when intestinal loss is extensive. The pathophysiology of short bowel syndrome, its aetiology, prognosis and our understanding of the mechanisms of adaptation are reviewed. Management by a multi-disciplinary nutritional care team is advocated and should be directed to the maintenance of growth and development, the promotion of intestinal adaptation, the prevention of complications and the establishment of enteral nutrition. The choice of enteral feed, the role of drugs and the use of pro-adaptive nutrients and agents are discussed. Complications including cholestasis and catheter related sepsis are outlined with strategies to reduce them. Finally the roles of secondary surgical interventions including transplantation are discussed.

GLP-2 augments the adaptive response to massive intestinal resection in rat

To determine whether treatment with a potent protease-resistant analog of human glucagon-like peptide 2 (GLP-2) might augment the adaptive response to massive intestinal resection, rats were divided into resected, which had 75% of the midjejunoileum removed, sham-resected, and nonsurgical groups. Within each group, animals were assigned to 21 days of treatment with the drug (0.1 micrograms/g of the GLP-2 analog in phosphate-buffered saline) or vehicle alone subcutaneously twice daily. Food intake; weight gain; jejunal and ileal diameters, total and mucosal wet weights per centimeter, crypt depths, and villus heights; mucosal sucrase activity, milligrams of protein per centimeter, and micrograms of DNA per centimeter; and D-xylose absorption were measured. There was a significant increase in diameter, total and mucosal wet weights per centimeter, crypt-villus height, sucrase activity, milligrams of protein per centimeter and micrograms of DNA per centimeter in both the jejunum and ileum in response to resection and a significant additive response to the GLP-2 analog in the jejunum but not in the ileum. The ratio of milligrams of protein per centimeter to micrograms of DNA per centimeter of mucosa was not different among groups, consistent with hyperplasia. D-Xylose absorption was significantly reduced in response to resection; however, the GLP-2 analog enhanced the absorptive capacity in control animals and restored the absorptive capacity in resected animals. Thus the GLP-2 analog induces mucosal hyperplasia and enhances the rate and magnitude of the proximal intestinal adaptive response to massive resection.

Prospective evaluation of faecal fatty acid excretion in short bowel syndrome in newborns

Short bowel syndrome (SBS) in the newborn results in limited intestinal absorptive capacity, leading especially to fatty acid (FA) malabsorption. It is unknown whether adaptation occurs in time in FA absorption, and whether this adaptation is chain-length dependent. The aid of the present study was to prospectively evaluate FA absorption and excretion during SBS in the newborn. Twenty-one neonates who underwent small bowel resection (of variable length) for various reasons (necrotizing enterocolitis, intestinal atresia, meconium peritonitis, cloacal extrophy, etc) were studied. Eight neonates had SBS, defined as a small bowel remnant of less than 50% of the original small bowel length related to gestational age. The mean remaining small bowel length in the SBS group was 34% (24% to 42%). The non-SBS control group consisted of 13 neonates who had only minor small bowel resections. The mean remaining bowel length for the non-SBS group was 95% (70% to 100%). The results show that the total fractional excretion of FA (FE-FA) at 2 weeks and 1, 2, 3, and 4 months postsurgery was 51% +/- 37%, 33% +/- 24%, 51% +/- 65%, 53% +/- 27%, and 7% +/- 2% in patients with SBS, versus 12% +/- 8%, 24% +/- 10%, 9% +/- 3%, 8% +/- 3% and 17% +/- 14% in the non-SBS controls, respectively (P < .05 by ANOVA). There appeared to be an amelioration in time in FA absorption, especially in the SBS group, after 3 months. FE-FA was chain-length related, being considerably less for C10 and C12 than for C14 and longer amounts. An amelioration of absorption occurred in the SBS patients, especially with the longer-chain FA. On the basis of the study data, the authors conclude that in the initial adaptation phase shorter chain lengths are better absorbed than longer chain lengths; however, in the latter FA group, substantial adaptation occurs with time.

Management of the short-bowel syndrome

The patient with short-bowel syndrome after massive small-intestinal resection represents one of the greatest clinical challenges a general surgeon must face. Maintaining optimal nutritional and metabolic support until maximum bowel adaptation can occur is the top priority of therapy. Currently, no operative procedure for adjunctive management of the short-bowel syndrome is sufficiently safe and effective to recommend its routine use. Long-term parenteral nutrition remains the cornerstone of successful management.

Regional difference in intestinal adaptation after total colectomy as judged by the changes of mucosal Na-K ATPase, cyclic AMP, and transmural potential difference

Intestinal adaptation and its regional difference after total colectomy were investigated in dogs by measuring mucosal Na-K ATPase, cyclic AMP, and transmural electric potential difference (PD). Twenty-four weeks after the total proctocolectomy, Na-K ATPase activity and PD increased significantly in all intestinal sites, whereas cyclic AMP showed no significant changes. The regional difference in the remaining intestine was examined in the jejunum, ileum, and interposed jejunum (neorectum). Na-K ATPase activity showed no significant regional difference, but the largest increase was found to occur in the ileum. PD also increased markedly in the ileum and there was significant difference between the ileum and other intestinal sites. These facts suggest that the increased active ion transport mediated by mucosal Na-K ATPase and transmural PD in the ileum is closely related to the intestinal adaptation occurring after total colectomy and indicates a greater potential of the ileum for adaptive compensation than either jejunum or neorectum.

Continuous enteral nutrition during the early adaptive stage of the short bowel syndrome

Sixty-two patients with the short bowel syndrome (30-150 cm) were managed by continuous enteral nutrition (CEN) in the early adaptive phase. In all, 82 per cent were referrals from other units and 85 per cent of referrals had failure of one or more organ systems on admission. There were intra-abdominal abscesses in 41 per cent of patients and 37 per cent had an enterocutaneous fistula. The diet included polysaccharides, medium chain triglycerides and protein hydrolysates, mixed with a high-viscosity tapioca suspension. An elemental diet was used initially in 15 per cent of patients. Thirty-three patients had an interruption of the gastrointestinal tract by a temporary enterostomy. Chyme was re-infused into the distal intestine in 20 cases. 'Zero-time' was taken as the time of operation or, for referred patients treated conservatively, the date of admission. CEN was commenced at a mean of 14 days from zero-time. Total parenteral nutrition could be discontinued at a mean of 36 days and exclusive oral alimentation was resumed at a mean of 87 days. Patients with small bowel longer than 80 cm attained enteral autonomy earlier than patients with a shorter length. Mean faecal volume did not increase following institution of CEN, suggesting tolerance to the high-viscosity diet. In cases with re-infusion of enteric content, the distal circuit (length of distal small intestine 46 cm) was able to absorb 70 per cent of the volume re-infused (mean volume 2700 ml). Body weight and nutritional markers increased significantly during the course of CEN. This study suggests that enteral autonomy can be attained early in the short bowel syndrome, even under challenging conditions. Elemental formulae do not appear to offer a benefit over polymeric diets.

Nutritional absorption in short bowel syndrome. Evaluation of fluid, calorie, and divalent cation requirements

Eight patients with a short bowel resulting from intestinal resection and clinically stable for at least one year were studied for 10 days. The diet chosen was lactose-free with a low fiber content and contained 22% of total calories as protein, 32% as carbohydrate, and 46% as fat. Total fluid volume was kept constant, and all patients were in positive nitrogen balance. During the 10-day period, blood chemical concentrations, stool, and/or ostomy volume, urine volume, electrolyte excretion, and calorie and divalent cation absorption were measured. In addition it was determined that fluid restriction during meals did not affect these parameters. In these patients the absorptions of fat, carbohydrate, protein, and total calories were 54%, 61%, 81%, and 62%, respectively. Similarly the absorption of the divalent cations, calcium, magnesium, and zinc, were 32%, 34%, and 15%, respectively. We suggest that patients with short bowel syndrome, who have been stable for at least one year and who can tolerate oral diets, do not need to restrict fat or to separate fluids from solids during their meals. Furthermore, they should increase their oral intake to 35-40 kcal/kg ideal body weight in order to counteract their increased losses. The diet should contain 80-100 g protein/day in order to maintain a positive nitrogen balance and a large margin of safety. In addition, these patients may take oral supplementation of calcium, magnesium, and zinc to maintain divalent cation balance.